This invention relates to a thermostatic valve for a coolant control of an internal-combustion engine, having a thermostatic working element which is assigned to the coolant flow and whose working piston is supported in an abutment which can be adjusted by means of another thermostatic working element which is to be arranged outside the coolant flow and is mounted on a valve housing part.
By means of a thermostatic valve of this type, which is known from the German Patent Document DE-A 32 26 104, the control range of the thermostatic valve becomes adjustable. The working element, which is mounted on the valve housing part and is to be arranged outside the coolant flow, serves as an adjusting member which, because of its arrangement, is subjected to the ambient air temperature, particularly the engine compartment air of a motor vehicle. As a result, it is possible, also in the case of changing environmental conditions, to regulate the desired coolant temperature and therefore the desired engine temperature. In this case, it is also known to provide an additional electric heating device for the working element serving as the adjusting member by means of which further control parameters can be entered into the control.
It is also known (German Patent Document DE-A 33 15 308) to separate the thermostatic working element serving as the adjusting element from the thermostatic valve and to connect it with the working piston of the working element to be arranged in the coolant flow by way of remote-transmission devices, such as a Bowden cable, or the like. A development of this type, on the one hand, results in increased constructional expenditures while, on the other hand, such transmission devices are in the way, particularly in the case of combustion engines of motor vehicles, and prevent the mounting of other elements.
A thermostatic valve for a coolant control of an internal-combustion engine is also known (WO 90/04088) which comprises a thermostatic working element situated in the coolant flow whose working piston is supported on an abutment which is formed by the working piston of another thermostatic working element. This thermostatic working element is provided with an electric heating device so that the moving-out of its working piston can be controlled as a function of outside parameters. This thermostatic working element is mounted on a valve housing part, being surrounded by a plastic housing and being held on the valve housing part by means of a plastic holder. In this case, its working piston projects into the interior of the valve housing part so that it is situated in the coolant flow. The expansion agent, which is housed in this working element, must be designed such that its expansion does not take place before temperatures are reached which are clearly higher than the possible temperatures of the coolant.
It is an object of the invention to improve a thermostatic valve of the initially mentioned type such that a more precise control effect is achieved.
This object is achieved according to preferred embodiments of the invention in that a connecting element made of a material which has a lower thermal conductivity than metal is arranged between the valve housing part and the working element to be arranged outside the coolant flow.
By means of this development, a thermal uncoupling is achieved between the parts which come in contact with the coolant and are therefore heated by the coolant and the thermostatic working element serving as the adjusting element. Because of this uncoupling, the thermostatic working element can carry out its control function without any interference by the temperature of the coolant. The thermostatic working element, which is to be arranged outside the coolant flow, is therefore subjected almost exclusively to the ambient temperature; that is, when used in motor vehicles, to the engine compartment temperature.
In a development of the invention, it is provided that the thermostatic working element is held on the housing part by means of a holder made of a heat-insulating material. This results in a simple construction since the holder of this thermostatic working element already causes the thermal uncoupling.
In a further development of the invention, it is provided that, between the working element to be arranged outside the coolant flow and the valve housing part, at least one shield is provided against radiant heat coming from the valve housing part. This is used for a further improvement of the thermal uncoupling.
In a further development of the invention, it is provided that the holder is provided on the outside with cooling ribs enlarging its surface. This also further improves the thermal uncoupling because a heat dissipation takes place by wa of the cooling ribs before this heat may reach the thermostatic working element. In this case, the cooling ribs may be developed such that they serve as a shield; that is, that they are disposed between the thermostatic working element and the valve housing part.
In a further development of the invention, it is provided that the working piston of the working element to be arranged outside the coolant flow serves as the abutment which is arranged coaxially with respect to the working element to be arranged in the coolant flow. This results in a simple and very compact construction. In an advantageous development, it is provided in this case that, between the working piston of the working element assigned to the coolant flow and the working piston of the working element to be arranged outside the coolant flow, an intermediate member is arranged which is made of a material having a lower thermal conductivity than metal. Thus, it is ensured that no thermal bridge is created also between the working pistons of the two thermostatic working elements by which a direct heat transmission may take place to the working element serving as the adjusting member.
In a further development of the invention, it is provided that the thermostatic working element is detachably mounted on the holder and that the holder is provided with sealing devices which are assigned to the working piston of the working element assigned to the coolant flow or to an intermediate member arranged between the two working pistons and remaining in the holder. As a result, it is possible to remove the thermostatic working element serving as the adjusting member without opening up the coolant circulation as a result. This development of the holder provides that no coolant can emerge even when the thermostatic working element is removed.
In a further development of the invention, it is provided that the working element to be arranged outside the coolant flow is supported against the moving-out direction of its working piston in the holder by means of a lift-over spring. This ensures that the danger of damage is avoided also in the case of an overheating.
In a further development of the invention, it is provided that the circumferential surface of the intermediate member is constructed as a control cam for an electric control element mounted on the holder. As a result, it becomes possible to influence, as a function of the control elements that are to be electrically switched, particularly the drive of a cooling fan which is assigned to a radiator of the coolant circulating system. It therefore becomes possible to stop one or several stages of the cooling fan so that the cooling fan is not switched on with these stages when an increased coolant temperature is desired.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.